Multiple Sclerosis

The translation gap between preclinical EAE studies and MS clinical trials is a persistent concern. Historically, EAE endpoint mismatches – motor scoring, weight loss, and acute inflammatory paralysis – do not translate cleanly to clinical MS outcome measures such as EDSS progression, MRI lesion burden, or brain atrophy. Visual endpoints close this gap more effectively than most other readouts because the clinical MS community has invested substantially in validating OCT-RNFL thinning, LCLA loss, and VEP latency prolongation as objective, quantitative biomarkers of neuroaxonal damage (Petzold et al., 2017, Lancet Neurol; Balcer et al., 2015, Neurology).

In EAE, the preclinical analogue to OCT-RNFL is retinal flat-mount RGC counting combined with optic nerve cross-section axon density – both terminal histological endpoints. The preclinical functional analogue to LCLA and VEP is OMR testing with OptoDrum: it measures the spatial frequency and contrast threshold of the retina-to-brainstem circuit, reflecting the combined structural integrity of the RGC, optic nerve, and accessory optic system. The OMR is not a cortical measure – it does not capture VEP latency directly – but for RGC and optic nerve axon integrity it provides a non-invasive, longitudinal, quantitative readout that complements terminal histology.

A key practical question is whether OptoDrum is sensitive enough to detect functionally meaningful between-group differences when an immunological variable is being tested rather than a large structural intervention. This has now been answered affirmatively across a range of immunological manipulations of EAE, including conditional immune gene knockouts.

A central problem in MS drug development is the inadequacy of most preclinical EAE models for progressive disease. Standard acute EAE captures relapsing-remitting neuroinflammation well but underrepresents the chronic diffuse axonal and grey matter attrition that defines SPMS and PPMS. Chronic-relapsing EAE variants, cuprizone-EAE combinations, and TMEV models partially address this, but all require long study durations (weeks to months) during which repeated, non-terminal functional endpoints are essential to avoid excessive animal numbers and to track the kinetics of neurodegeneration accurately.

A further challenge is identifying which environmental or metabolic variables accelerate the progressive axonal loss phase. Diet, gut microbiome, and systemic metabolic state are clinically relevant modifiers of MS progression, but their impact on preclinical visual pathway outcomes had not been directly quantified with a functional endpoint until recently. Understanding how these variables interact with the EAE model is essential for designing preclinical MS studies that are representative of the patient populations in clinical trials.

For a dedicated treatment of axonal degeneration mechanisms and their functional readouts, see Axon Degeneration and Optic Nerve Damage.

Preclinical benchmarking of MS disease-modifying therapies (DMTs) requires an endpoint that is (a) sensitive to partial protection rather than only complete rescue, (b) non-terminal to enable longitudinal within-animal efficacy tracking, and (c) clinically translatable so that preclinical effect sizes can be compared with clinical trial outcomes. Motor scoring in EAE fails on (c); histological RGC counting fails on (b); ERG and VEP require anaesthesia and surgical preparation, limiting longitudinal repeat measurements. The OMR measured by OptoDrum satisfies all three criteria for the visual pathway.

Among the current generation of approved MS DMTs, B cell-depleting agents (ocrelizumab, ofatumumab, ublituximab) are particularly important to model preclinically because their mechanism – anti-CD20-mediated B cell depletion – is now the standard of care for both RRMS and PPMS. FcRn blockade (rozanolixizumab, nipocalimab) is a next-generation strategy being evaluated in MOGAD and MS variants where pathogenic IgG clearance is the therapeutic target. BTK inhibitors (evobrutinib, tolebrutinib, fenebrutinib) are currently in Phase 3 MS trials; they target both B cells and microglia, making visual pathway endpoints in EAE directly relevant to their CNS efficacy readouts.

HIF-1 inhibition with acriflavine represents a mechanistically distinct category: targeting the metabolic-hypoxic component of demyelinating lesions rather than the adaptive immune response. This is increasingly relevant to progressive MS where tissue hypoxia in lesions contributes to axonal loss independent of acute inflammation.

Anti-CD20 B cell depletion (ocrelizumab for RRMS and PPMS, ofatumumab for RRMS) is now the most effective class of MS DMT available. Yet the preclinical models used to justify early B cell targeting experiments were largely T cell-centric: standard MOG_35-55 EAE in C57BL/6 mice does not generate substantial MOG antibody titres and therefore does not fully recapitulate the humoral immune compartment of human MS. Developing B cell-dependent EAE models that generate authentic antibody responses alongside T cell-driven demyelination is a prerequisite for meaningful preclinical evaluation of ocrelizumab analogues, Bruton tyrosine kinase (BTK) inhibitors, and next-generation B cell-targeting strategies.

FcRn blockade is a complementary approach: rather than depleting B cells, it accelerates IgG catabolism by blocking the neonatal Fc receptor responsible for IgG recycling. This is clinically relevant for MOGAD-spectrum disease and for MS patients with high pathogenic antibody burdens. Evaluating FcRn blockade in EAE requires a model that actually produces pathogenic antibodies – which the standard T cell-driven model does not. Visual endpoints are particularly useful in these humoral models because optic neuritis severity correlates with antibody-mediated complement activation and direct axonal attack, making OMR measurements a sensitive read of antibody-driven pathology at the optic nerve.

For the MOGAD spectrum specifically, see Autoimmune Demyelinating Diseases, which covers the full spectrum from MS to NMOSD and MOGAD.

Clinical MS is not only a white matter tract disease: grey matter atrophy, cortical demyelination, and synaptic loss in visual cortex (V1, MT/V5) contribute substantially to visual disability in RRMS and particularly in SPMS. Clinical assessments of cortical visual function include VEP latency (cortical processing time), high-level pattern recognition tasks, and psychophysical contrast sensitivity at high spatial frequencies – all of which require an intact visual cortex. Low-contrast visual acuity, as measured by the LCLA test in clinical trials, engages cortical processing at threshold; it is not purely a subcortical reflex measure.

In preclinical MS research, distinguishing subcortical (retino-brainstem) from cortical visual consequences requires two complementary endpoint strategies. The OptoDrum optomotor reflex provides information about the retina-to-brainstem pathway: it is sensitive to RGC loss, optic nerve axon damage, and reduced retinal signal transmission, but insensitive to isolated cortical dysfunction if the upstream pathway is intact. AcuiSee, by contrast, requires the animal to make an operant visual discrimination that engages visual cortex: it is therefore the appropriate endpoint when cortical grey matter atrophy, white matter lesions in the optic radiation, or direct cortical demyelination is the research question. Using both instruments in the same EAE study enables a functional dissection of where along the visual pathway MS pathology is exerting its dominant effect at any given disease stage.